GCSE Astronomy — Exploring Starlight

Led by Annie Jump Cannon

Module 13 of Edexcel GCSE Astronomy — the second-largest in the spec at 35 points. Led by Annie Jump Cannon, who classified more than 225,000 stellar spectra by hand and built the OBAFGKM scheme that remains the foundation of stellar classification today. The student moves from the magnitude scale and distance modulus through stellar spectra, the OBAFGKM sequence, the Hertzsprung-Russell diagram, parallax, and the variable-star families that calibrate the cosmic distance ladder.

1. Module 13

   Exploring Starlight

   Led by Annie Jump Cannon

   The question

   How is the brightness of a star measured, what does its spectrum reveal, how is it classified, where does it sit on the Hertzsprung-Russell diagram and what does its position there tell us about its life cycle, how is its distance determined by parallax or by spectroscopic methods, and what do the light curves of variable stars — eclipsing binaries, Cepheids, novae, supernovae — reveal? The spec asks for the magnitude scale, the distance modulus, the OBAFGKM classification, the H-R diagram, parallax and the parsec, and the analysis of variable-star light curves including the use of Cepheids as standard candles.

   Outcome

   the student can apply the magnitude scale and distance modulus, account for what stellar spectra reveal, classify by OBAFGKM spectral type, sketch a labelled Hertzsprung-Russell diagram and locate the main populations, account for low-mass and high-mass stellar life cycles upon it, determine distances by parallax (d = 1/p) and by spectroscopic parallax, and analyse the light curves of all required variable star families. *(Edexcel 1AS0 Paper 2 — Topic 13, spec points 13.1–13.19)*

   Sub-units

   1. ○ 13.1 Apparent and absolute magnitude; the distance modulus Open this unit → ✓ ↻
   2. ○ 13.2 Stellar spectra: composition, temperature, radial velocity Open this unit → ✓ ↻
   3. ○ 13.3 The OBAFGKM classification scheme Open this unit → ✓ ↻
   4. ○ 13.4 The Hertzsprung-Russell diagram and stellar life cycles Open this unit → ✓ ↻
   5. ○ 13.5 Inverse-square law, the parsec, and heliocentric parallax Open this unit → ✓ ↻
   6. ○ 13.6 Spectroscopic parallax via the H-R diagram Open this unit → ✓ ↻
   7. ○ 13.7 Variable stars: eclipsing binaries, Cepheids, novae, supernovae Open this unit → ✓ ↻
   8. ○ 13.8 Cepheids as standard candles Open this unit → ✓ ↻
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